tl;dr: the odds are against relationships that start in your teens for LOTS of good reasons. If you think you are going to be the exception to the statistics, you should have a very clear understanding of how your relationship is different. "We love each other so much" does not qualify, nor does "He's always there for me" or "they are my best friend", etc. "We survived the civil war in Syria" is more like what I'm talking about. It sounds condescending but it is really just the honest truth that young people mostly don't know what's important in relationships. My view is that most relationships that start young and don't end are that they are emotionally co-dependent in some way. (In my case, mostly, I was shy and she was socially competent.)
The details of my statistically probable relationship failure:
I am 45 and my wife and I started dating at 17. We currently have 3 kids in grade school/high school, and have been separated for about 6 months. (Hopefully, from my perspective) we will be divorced in a year or so.
We were both raised catholic and took it to heart to some extent. Different Catholic grade schools for both of us, and different same sex Catholic high schools. We met through mutual friends in high school.
We lost our virginity to each other around 17ish, and had car sex once a week or so through the rest of high school. We went to separate colleges - broke up for a few months freshman year and then got back together and had an LTR. My college was a technical college and there were about 3 guys per girl at the time. I'm shy-ish and had no dating/girl experience and there were no 'close calls' cheating-wise.
We basically had the sex life of sexually shamed Catholic high school-ers until we were about 40. Little foreplay missionary we both came and it was done. I was always happy when it was time to have another kid because it meant I would get laid several times a month for 2 or 3 months. A big factor here was the religious guilt I felt for masturbating, so I was 'dependent' on her for orgasms I didn't regret. And of course that turned her into a fleshlight for me, basically. At 40, I had gotten to the point where I had (but didn't realize) major depressive disorder and suicidal ideations due to my sexual problems but also more related to what, in retrospect, were obvious and serious relationship problems.
I found r/deadbedrooms and r/sex via r/gonewild (I got over my masturbation guilt) and got sex positive and sexually educated and came out to my wife as heterosexual and we worked on things a lot and got to the point where the sex was pretty good.
Ultimately I couldn't get over the resentment of the years of unhappiness and recognized that, from a couple/relationship perspective, we were very incompatible and I'd never be really honestly happy, and so I left her.
She's slowly trying to put herself back together because she was very happy with our life and looking forward to spending the rest of it with me, and I'm trying to work through my feelings of regret and loss for the decades in a relationship I never really enjoyed.
My suggestion: if you are really right for each other, break up, go have some independent life, and then get back together at 25 or so and if there is still that spark, you've got a solid foundation for the rest of the life you were meant to have together.